In a conventional web-fed printing press, a web of material, for example, comes off a web roll into an infeed mechanism and then passes through one or more printing units followed by downstream processing units. The downstream processing units may include, among other units, a dryer, a chill unit, a slitter, a cutter, a perforator and/or a folder which includes an angle bar section, a deceleration unit, and a stacker. In the folder, individual printed products, referred to as signatures, are formed and prepared for further processing, such as binding, to form a final printed product. A sheet-fed press, on the other hand, feeds individual sheets through print units, dryers, a chill unit, and other possible processing units, before eventually folding and/or stacking the sheets. The sheet-fed press does not require a cutter in the same manner as a web-fed press which requires the web to be cut for processing, however, both types of presses transport signatures as a stream of printed products during press operation.
A stream of printed products may be gripped by a gripper conveyor as is commonly known in the art. It is often desirable to process this stream of products by, for example, splitting it into two or more separate streams or some other processing such as conveying and stacking. The conventional method of splitting a stream of products, especially printed products, is to drag the initial stream over a vacuum belt traveling slower than the conveying system and to release every other (i.e., second) signature from a gripper conveyor as soon as the respective signature contacts the vacuum belt. However, this often results in relative movement between those signatures delivered onto the vacuum belt and those signatures which remain gripped by the conveying system. Consequently, correct alignment and fixed pitch (the distance between like points of two consecutive signatures in a product stream) of the signatures delivered to the vacuum belt cannot be guaranteed.
A number of patents purport to describe grippers which are used for transporting signatures and for purposes other than splitting a product stream. For example, U.S. Pat. No. 4,550,822 purports to disclose an apparatus for transporting flat products, especially printed products. In this configuration each gripping unit comprises a stationary clamping jaw, a pivotable clamping jaw and a plate shaped stop. The pivotable clamping jaw is pivoted against the action of a closing spring by a cam structure or the like. The products are first accelerated and then pushed into the open gripper mouth until they abut the stop so that the printed products are aligned at the region of their leading edges. At their trailing edges the printed products remain under the conveying action of the belt conveyor at least until the gripper units are closed.
U.S. Pat. No. 4,072,228 purports to show an apparatus for evening a stream of printed products. This apparatus comprises a number of revolving entrainment members being in a drag connection with one another. At the region of their conveying action path the entrainment members are guided and at the start of their path driven by a thrust drive and at the end thereof driven by a traction drive. The entrainment members engage the printed products and the thrust and traction drives cause a change in the spacing of the entrainment members and consequently, in the spacing of the products.
U.S. Pat. No. 3,809,214 purports to disclose a turning conveyor for flat structures, especially printed products. This turning conveyor encompasses a plurality of entrainment members which move along with the flat structures and each of which can be brought into engagement with a respective one of the flat structures. The entrainment members are controlled such that at least at the time they are in engagement with a flat structure they carry out a relative movement with regard to the direction of movement of the main conveyor in order to turn the flat structures about an axis being perpendicular to the flat structures. In addition, gripper conveyors, such as the type described in co-pending application U.S. Ser. No. 08/504,868, filed Jul. 20, 1995, which is incorporated herein by reference, transport signatures for processing in a printing press.
Several other approaches have been attempted to reduce or eliminate problems associated with handling the signatures in a printing press, but none have been entirely successful. One attempted solution, for example, was to grip signatures individually in a leading edge configuration, however, problems remained with aerodynamic and mechanical disturbances causing handling and transporting difficulties. For example, lift and drag forces can operate upon signatures being transported to, for example, lift the edge of a signature and fold the edge back or separate pages of the signature.